1. Field of the Invention
This invention relates to a light wave range finder in which a range finding optical system includes an integrated circuit. From another aspect, it relates to a light integrated circuit type light intensity modulator which is used in the light wave range finder. From a further different aspect, it relates to an optical path switching device which is used in the light wave range finder.
2. Description of the Prior Art
Heretofore, there has been known a light wave range finder including a bulk type range finding optical system as shown in FIG. 14. In FIG. 14, LD denotes a semiconductor laser, 100 denotes a chopper, 101 denotes a reflecting prism which constitutes a part of an external range finding optical path I, 102 denotes an objective lens, 103 and 104 each denotes a total reflection mirror which constitutes a part of an internal reference optical path II, 105 denotes a lens which is disposed between the total reflection mirrors 103 and 104, 106 denotes a half mirror, and 107 denotes a light receiving element.
The semiconductor laser LD emits a coherent beam of light which is modulated in intensity. The chopper 100 has such a function as to switch the intensity modulated coherent beam of light between the external range finding optical path I and the internal reference optical path II. The light wave range finder is provided with a chopping motor (not shown) for driving the chopper 100.
The intensity modulated coherent beam of light is selected by the chopper 100 and guided either to the external range finding optical path I or the internal reference optical path II. The coherent beam of light guided to the external range finding optical path I is reflected by the reflecting prism 101 and guided to a corner cube (not shown) disposed at an observation point through the objective lens 102. Then, the coherent beam of light guided to the external range finding optical path I is reflected by the corner cube to return in the direction where the objective lens 102 is located and guided to the light receiving element 107 through the reflecting prism 101 and the half mirror 106. The coherent beam of light guided to the internal reference optical path II is guided to the light receiving element 107 through the total reflection mirror 103, the lens 105, the total reflection mirror 104 and the half mirror 106.
A distance to the observation point is measured or found in the following manner. First, the delay of the phase of the coherent beam of light arriving at the light receiving element 107 via the external range finding optical path I is digitally counted. Next, the delay of the phase of the coherent beam of light arriving at the light receiving element 107 via the internal reference optical path II is digitally counted. The distance to the observation point is measured or found by such counting as just mentioned. Errors caused by time delay of the internal reference optical path II and the electronic circuit are removed.
However, in the conventional light wave range finder, a chopping motor is necessary in order to switch the internal reference optical path II and the external range finding optical path I. Also, an ND filter of a variable density is required in order to regulate the amount of light. Accordingly, the conventional range finder requires many mechanical operating portions and lacks stability and reliability. Furthermore, the conventional range finder has the shortcomings in that the finder itself becomes large in size, that the finder is difficult to be regulated because of the large number of optical parts and that the cost becomes high.
Moreover, since the conventional range finder is constituted as such that the intensity of light is modulated by modulating the driving electric current of the semiconductor laser, the accuracy of the range finding is likely to decrease due to fluctuation of the oscillating wave length. Since the upper limit of the modulation frequency is about 1 GH.sub.Z in view of the speed of response, a high speed modulation is difficult to expect.
Next, regarding a light integrated circuit type modulator, there is a known one which uses a branch coherent type optical switch. In this conventional modulator, a coherent light propagating through an incident light guiding wave path is bisected by a Y-branched guiding wave path. The bisected coherent light is guided through a first and a second wave guiding paths and converged at an outgoing light guiding wave path and then taken off as an outgoing light. If the difference of phase of the coherent light guided through the first and the second guiding wave paths becomes .pi., an outgoing light from the outgoing light guiding wave path is extinguished due to the interference or coherence. Therefore, in this conventional modulator, at least one of the first and the second guiding wave paths is provided with an electrode as optical path length changing means for changing an optical path, and the electrode is controlled such that the difference of the phase of the coherent light becomes .pi..
However, a conventional light integrated circuit type intensity modulator has the shortcoming in that although the modulation frequency can be established, the light amplitude cannot be regulated.